U.S. Pat. Nos. 3,505,6 and Re 28,328 disclose test probes of the type having a pair of electrical contacts at its forward end, a central body member, and a movable sleeve located around the central body member. The sleeve is movable axially to forward and rearward positions relative to the central body member to cause latch means to be moved to latching and unlatching positions. The purpose of the latch means is to latch the probe inside of a breech cap while testing is being carried out. Problems sometimes occur, however, in that the sleeve may be accidently moved to its rearward position resulting in the probe being removed from the breech cap.